1. Field of the Invention
The present invention relates to a piezoelectric actuator which is used in an apparatus such as a liquid transporting apparatus.
2. Description of the Related Art
A piezoelectric actuator which drives an object by using a deformation (piezoelectric distortion) of a piezoelectric material layer when an electric field acts, has hitherto been known. For example, in Japanese Patent Application Laid-open No. 2006-181958 (FIG. 7), a piezoelectric actuator which is provided to an ink-jet head which jets an ink from nozzles has been described.
The piezoelectric actuator described in Japanese Patent Application Laid-open No. 2006-181958 is an actuator which is arranged on one surface of a channel unit in which, ink channels including nozzles and pressure chambers are formed, and which makes the ink be jetted from the nozzles by applying a pressure to the ink in a pressure chamber. More concretely, the piezoelectric actuator is made of a piezoelectric ceramics material such as lead zirconate titanate (PZT), and has a plurality of piezoelectric sheets stacked on the one surface of the channel unit to cover the pressure chambers, and two types of electrodes (individual electrodes and common electrode) which are arranged on the piezoelectric sheet positioned at the uppermost layer, on both surfaces of a portion facing the pressure chamber. Moreover, the piezoelectric actuator is structured such that when an electric voltage (electric field) is applied between the two types of electrodes, due to a deformation of an active portion of the piezoelectric material layer, an inactive piezoelectric sheet on a lower side thereof is deformed to form a projection toward the pressure chamber, and the pressure is applied to the ink inside the pressure chamber.
Such piezoelectric actuator is manufactured by the following process. Firstly, after the electrodes are formed on the surface of the plurality of unsintered piezoelectric sheets (green sheets), these piezoelectric sheets are stacked, and a stacked body of the piezoelectric sheets is sintered. Moreover, after applying an adhesive to one surface of the stacked body of the sintered stacked body, the stacked body is pressed against the channel unit (cavity plate) in which the pressure chambers open, and is joined to the channel unit.
However, when the sintered stacked body of the piezoelectric sheets is pressed against the surface of the channel unit in which the pressure chambers which are opened are formed, a stress of the stacked body is concentrated particularly at a portion facing an edge portion of the pressure chamber. Moreover, the piezoelectric sheet made of a ceramics material has a high brittleness after sintering. Furthermore, from a point of view of electric power consumption, the piezoelectric sheet is formed to be thin such that the piezoelectric sheet can be deformed substantially by as low voltage as possible. Therefore, at the locations where the stress is concentrated, a frequency of occurrence of damage such as breaking and cracking of the piezoelectric layer becomes high, which has been a cause of a reduction in the yield.